Mirage in the sky: Nonthermal dark matter, gravitino problem, and cosmic ray anomalies

Abstract

Recent anomalies in cosmic rays could be due to dark matter annihilation in our galaxy. In order to get the required large cross section to explain the data while still obtaining the right relic density, we rely on a nonstandard thermal history between dark matter freeze out and big-bang nucleosynthesis. We show that through a reheating phase from the decay of a heavy moduli or even the gravitino, we can produce the right relic density of dark matter if its self-annihilation cross section is large enough. In addition to fitting the recent data, this scenario solves the cosmological moduli and gravitino problems. We illustrate this mechanism with a specific example in the context of $U(1{)}_{B\ensuremath{-}L}$ extended minimal supersymmetric standard model where supersymmetry is broken via mirage mediation. These string motivated models naturally contain heavy moduli decaying to the gravitino, whose subsequent decay to the LSP can reheat the Universe at a low temperature. The right-handed sneutrino and the $B\ensuremath{-}L$ gaugino can both be viable dark matter candidates with a large cross section. They are leptophilic because of $B\ensuremath{-}L$ charges. We also show that it is possible to distinguish the nonthermal from the thermal scenario (using Sommerfeld enhancement) in direct detection experiments for certain regions of parameter space.